Government regulations require vehicles be configured to perform self-diagnostic testing of the evaporative emission (EVAP) system on the vehicle. Typically, vacuum pressure generated by a running engine is used to create certain conditions in the EVAP system so diagnostic testing can be performed. However, some engines are configured to automatically stop and restart to increase fuel economy. For example, when the vehicle is stopped at a traffic light, the engine may automatically stop running. Then, when the driver releases the brake pedal or presses the accelerator pedal because the traffic light turned green, the engine restarts automatically. This automatic stopping and restarting (i.e. stop-start operation) of the engine may interrupt the diagnostic testing of the EVAP system because the source of vacuum pressure is lost when the engine stops. As such, frequent stopping of the engine may make it difficult to perform the required diagnostic testing of the EVAP system if the system relies on a running engine to provide the vacuum pressure necessary for diagnostic testing.